Polishing slurry and method of polishing using the same

ABSTRACT

Disclosed are a polishing slurry used in a polishing process of tungsten and a method of polishing using the same. The slurry includes an abrasive for performing polishing and an oxidation promoting agent for promoting the formation of an oxide. The abrasive includes titanium oxide particles.

TECHNICAL FIELD

The present disclosure relates to a polishing slurry used in a polishing process of a metal and a method of polishing using the same, and more particularly, to a polishing slurry used in a chemical mechanical polishing process in a semiconductor manufacturing process, especially in a planarization process of a tungsten metal layer and a method of polishing using the same.

BACKGROUND ART

As the size of semiconductor devices gradually decreases and the number of metal wirings gradually increases, a surface unevenness on each layer is transferred to a next layer and so, the surface unevenness of a lowermost layer becomes significant. The unevenness sometimes seriously affects the formation of a desired layer in a next step. Accordingly, in order to improve the yield of the semiconductor devices, for example, to reduce a resistance deviation of a wiring during manufacturing the semiconductor devices, an application of a planarization process for removing the surface unevenness generated during performing various processes is essential.

As the planarization process, examples include a method of reflowing after forming a deposition layer, an etch-back method or a chemical mechanical polishing (CMP) process after forming the deposition layer, etc.

The CMP process is a process of contacting a surface of a semiconductor wafer with a polishing pad, and polishing while rotating the polishing pad and applying a slurry including an abrasive and various compounds to planarize the surface of the wafer. That is, a surface of a substrate or a layer on the substrate is chemically and mechanically polished to be planarized by the slurry and the polishing pad. Generally, the metal CMP process for polishing a metal is known to be performed by repeating a forming process of a metal oxide by an oxidizing agent and a removing process of thus formed metal oxide by the abrasive.

A tungsten CMP process for polishing tungsten widely used as a wiring of a semiconductor device is also performed by a repeated cyclic polishing mechanism of a forming process of tungsten oxide (WO₃) by using an oxidizing agent or an oxidation promoting agent, and a removing process of tungsten oxide by using an abrasive. Therefore, in order to increase a polishing efficiency, the formation of the tungsten oxide by adding the oxidizing agent and the efficient removing of the tungsten oxide by the abrasive are important. However, colloidal silica, the abrasive widely used conventionally, is not efficient in removing the tungsten oxide because a concentration dependency of the oxidizing agent is high. In addition, defects such as dishing or erosion are frequently generated when polishing a substrate including a pattern such as a trench. Once the dishing or the erosion is generated, an operation property of a device would be negatively influenced including a malfunctioning of a subsequently manufactured device.

Korean Patent publication No. 10-0948814 discloses a method of performing a polishing including two steps for decreasing the generation of the dishing and the erosion. In this case, a plurality of slurry is required to be prepared and a plurality of process is required to be performed. Accordingly, the process is complicated and a productivity is decreased.

DISCLOSURE OF INVENTION Technical Problem

The present disclosure provides a slurry for polishing tungsten and a polishing method of a substrate using the same.

The present disclosure also provides a slurry for polishing tungsten having a good selectivity on tungsten with respect to an insulating layer and a polishing method of a substrate using the same.

The present disclosure further provides a slurry for polishing tungsten decreasing the generation of dishing and erosion and a polishing method of a substrate using the same.

Solution to Problem

In accordance with an exemplary embodiment, a slurry for polishing tungsten comprises an abrasive for performing the polishing and an oxidation promoting agent for promoting formation of an oxide. The abrasive comprises particles of titanium oxide.

In example embodiments, the amount of the titanium oxide may exceed approximately 0.2 wt % and approximately 10 wt % or less based on the total amount of the slurry.

In example embodiments, the oxidation promoting agent may be one selected from the group consisting of ferric nitrate, potassium ferricyanide, iron chloride, iron sulfate, iron fluoride, iron bromide, copper chloride, copper fluoride, and copper bromide, and an amount of the oxidation promoting agent may be approximately 0.002 wt % to approximately 0.1 wt % based on the total amount of the slurry.

In example embodiments, the amount of titanium oxide may be approximately 0.7 wt % to approximately 5 wt % based on the total amount of the slurry.

In example embodiments, the amount of the oxidation promoting agent may be approximately 0.01 wt % to approximately 0.1 wt % based on the total amount of the slurry.

In example embodiments, pH of the slurry may be controlled to approximately 1 to approximately 4.

In example embodiments, the slurry may further include at least one oxidizing agent for forming an oxide selected from the group consisting of hydrogen peroxide, carbamide peroxide, ammonium persulfate, ammonium thiosulfate, sodium hypochlorite, sodium periodate, sodium persulfate, potassium iodate, potassium perchlorate, and potassium persulfate, and an amount of the oxidizing agent may be approximately 0.5 wt % to less than approximately 5.0 wt % based on the total amount of the slurry.

In example embodiments, the amount of the oxidizing agent may be approximately 0.5 wt % to approximately 2 wt % based on the total amount of the slurry.

In example embodiments, the slurry may further include at least one selectivity improving agent selected from the group consisting of polyvinyl pyrrolidone, vinyl pyridine and vinyl pyrrolidone.

In example embodiments, an amount of the selectivity improving agent may be approximately 0.05 wt % to less than approximately 3.0 wt % based on the total amount of the slurry.

In example embodiments, the particles of titanium oxide may be formed to have a crystalline phase and a mean primary particle size may be approximately 10 nm to approximately 100 nm.

In accordance with another exemplary embodiment, a slurry for polishing tungsten comprises particles of titanium oxide as an abrasive for performing polishing. The particles of titanium oxide have a crystalline phase and at least a portion of the particles of titanium oxides has an anatase crystalline phase. The particles of titanium oxide have a mean primary particle size of approximately 10 nm to approximately 100 nm.

In example embodiments, the particles of titanium oxide may have a polyhedron shape.

In example embodiments, the particles of titanium oxide may have the mean primary particle size of approximately 15 nm to less than approximately 50 nm.

In example embodiments, the particles of titanium oxide may include the anatase crystalline phase and a rutile crystalline phase. An amount of the anatase crystalline phase may exceed 50 based on 100 of a total of the anatase and the rutile crystalline phases.

In example embodiments, an amount of the titanium oxide may exceed approximately 0.2 wt % and approximately 10 wt % or less based on the total amount of the slurry.

In example embodiments, the slurry may further include an oxidation promoting agent for promoting forming an oxide and a pH adjusting agent.

In accordance with further another exemplary embodiment, a method of polishing a substrate comprises preparing a substrate including a tungsten layer formed thereon, preparing a first slurry comprising particles of titanium oxide as an abrasive, and a oxidation promoting agent, and polishing the tungsten layer while supplying the first slurry onto the substrate. The polishing is performed by forming a tungsten oxide layer on an upper surface of the tungsten layer and then, polishing the tungsten layer and the tungsten oxide layer through a penetration of at least a portion of the particles of titanium oxide into the tungsten oxide layer.

In example embodiments, an oxidizing agent may be supplied onto the substrate while supplying the first slurry onto the substrate.

In example embodiments, a selectivity improving agent may be supplied onto the substrate while supplying the first slurry onto the substrate.

In example embodiments, the selectivity improving agent or the oxidizing agent may be supplied onto the substrate through a separate inlet line from the first slurry.

In example embodiments, the oxidation promoting agent may include iron nitrate and the oxidizing agent may be hydrogen peroxide.

In example embodiments, a thickness of the tungsten oxide layer may be kept to a certain thickness while performing the polishing.

In example embodiments, at least a portion of the particles of titanium oxide may directly contact the surface of the tungsten layer while performing the polishing.

In example embodiments, the preparing of the substrate including the tungsten layer formed thereon may be performed by forming an insulating layer on the substrate, forming a trench in the insulating layer, and forming the tungsten layer on a whole surface of the insulating layer including the trench.

Advantageous Effects of Invention

In accordance with exemplary embodiments, titanium oxide may be used as an abrasive and a polishing process may be performed by directly contacting the titanium oxide onto the tungsten. Accordingly, a polishing efficiency with respect to tungsten may be largely increased and a polishing process exhibiting a high polishing selectivity on the tungsten with respect to an insulating layer may be accomplished.

The slurry in accordance with exemplary embodiments may remarkably decreased the generation of dishing and erosion generated during the conventional cyclic polishing. Particularly, a polishing process without generating the dishing may be accomplished.

In addition, the slurry in accordance with exemplary embodiments may be prepared by a simple method, and may efficiently polish tungsten through a simple CMP process. Accordingly, a device operating characteristic and reliability of semiconductor devices may be improved and a manufacturing productivity of the semiconductor devices may be improved.

BRIEF DESCRIPTION OF DRAWINGS

Exemplary embodiments can be understood in more detail from the following description taken in conjunction with the accompanying drawings, in which:

FIGS. 1 a to 1 d are photographic diagrams of the conventional polishing particles and polishing particles in accordance with an exemplary embodiment taken by using a transmission electron microscopy;

FIG. 2 is an X-ray diffraction analysis graph of polishing particles in accordance with an exemplary embodiment;

FIGS. 3 a to 3 d illustrate conceptual diagrams showing a polishing process using the conventional polishing particles;

FIGS. 4 a and 4 b illustrate conceptual diagrams showing a polishing process using polishing particles in accordance with an exemplary embodiment;

FIGS. 5 a to 5 c illustrate graphs showing polishing results obtained by the conventional method and exemplary embodiments of the present inventive concept;

FIG. 6 is a conceptual diagram illustrating a substrate including a pattern formed thereon;

FIG. 7 is a conceptual diagram for explaining dishing and erosion generated during polishing a substrate including a pattern formed thereon;

FIG. 8 is a photographic diagram on a substrate including a pattern formed thereon in accordance with an exemplary embodiment taken by a scanning electron microscopy;

FIG. 9 is a graph illustrating polishing results obtained by the conventional method and an exemplary embodiment of the present inventive concept;

FIGS. 10 a to 10 d illustrate photographic diagrams showing polishing results obtained by the conventional method and taken by a scanning electron microscopy;

FIGS. 11 a to 11 d illustrate photographic diagrams showing polishing results obtained in accordance with Embodiment 1 and taken by a scanning electron microscopy; and

FIGS. 12 a to 12 d illustrate photographic diagrams showing polishing results obtained in accordance with Embodiment 2 and taken by a scanning electron microscopy.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, specific embodiments will be described in detail with reference to the accompanying drawings. The present invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. In the figures, like reference numerals refer to like elements throughout.

A slurry in accordance with exemplary embodiments of the present inventive concept is a slurry for polishing tungsten and includes an abrasive for performing the polishing and an oxidation promoting agent for promoting the formation of an oxide. The abrasive includes particles of titanium oxide. The abrasive and the oxidation promoting agent are included in a solution. Particularly, the oxidation promoting agent dissolves in water, specifically in de-ionized (DI) water and the abrasive is dispersed in the water. In addition, the slurry may include a pH adjusting agent to adjust the pH of the slurry. The slurry has a dispersed state of a solid (abrasive) in a liquid and the amounts of each component are appropriately controlled.

As the slurry, other components separate from the first slurry including the above-described components, may be used separately during performing the polishing process. That is, an oxidizing agent, a selectivity improving agent stored in separate vessels from the first slurry may be included in the slurry.

Titanium oxide, the abrasive, is present as solid particles and is prepared as a crystalline phase of a polyhedron shape. Titanium oxide is an oxide compound of titanium metal and includes titanium dioxide (TiO₂). As illustrated in photographic diagrams taken by using a transmission electron microscopy in FIGS. 1 a to 1 d, the conventionally and widely used silica as the abrasive has an amorphous phase and the shape of the particle is spherical (refer to FIGS. 1 a & 1 b), however, the titanium oxide polishing particles in accordance with an exemplary embodiment has a crystalline phase and has a polyhedron shape including a facet (refer to FIGS. 1 c & 1D). Referring to FIG. 2 illustrating an X-ray diffraction analysis graph of the titanium oxide polishing particles, the particles of the titanium oxide has a crystalline phase. Since the polishing particles of the titanium oxide has the crystalline phase and the facet, the polishing of tungsten may be efficiently performed. Detailed description concerning above will be given hereinafter.

The mean primary particle size of the polishing particles of the titanium oxide is in a range of approximately 10 nm to approximately 100 nm. When the mean size of the polishing particles of the titanium oxide is less than approximately 10 nm, a polishing rate is low and the polishing of the tungsten becomes difficult, and when the mean size of the polishing particles of the titanium oxide exceeds approximately 100 nm, scratches may be generated during performing the polishing. In addition, the mean primary particle size of the polishing particles of the titanium oxide may be in a range of approximately 15 nm to approximately less than approximately 50 nm. Within the range, the concentration of the polishing particles may be optimized to achieve a high polishing ratio while minimizing the generation of the scratches.

In addition, at least a portion of the polishing particles of the titanium oxide includes an anatase crystalline phase and the polishing particles may include the anatase crystalline phase much more than other crystalline phases. Particularly, the polishing particles of the titanium oxide includes the anatase phase and a rutile phase, and may include the anatase phase much more than the rutile phase. Particularly, when the sum of the polishing particles of the titanium oxide having the anatase phase and the rutile phase is set to 100, the amount of the polishing particles having the anatase phase may be 55 or more. Generally, three variants having different crystal structures are known for the titanium oxide, including a rutile type stable at a high temperature, an anatase type stable at a low temperature, and a brookite type stable at a medium temperature. The rutile type has a good chemical resistance and is strong with respect to heat, however, has a hardness of approximately 6 to approximately 6.5 larger than that of the anatase type and is difficult to prepare. The anatase type is easy to prepare and has a smaller hardness of approximately 5.5 to approximately 6 when compared to the rutile type. The hardness of a tungsten oxide layer formed at a surface portion thereof during polishing the tungsten is approximately 5 to approximately 6 and the hardness of a silicon oxide layer as an insulating layer, underlying tungsten is approximately 6 to approximately 7. In order to increase a polishing rate of the tungsten oxide layer and the silicon oxide layer, the polishing particles having a high hardness, that is, the rutile type is desired. However, when the polishing particles include only the rutile type, the polishing rate is too high and so scratches are generated. In addition, a large portion of the silicon oxide layer may be removed to generate erosion. Accordingly, the anatase type polishing particles having a relatively low hardness when compared to the rutile type but having a sufficient hardness for polishing the tungsten oxide layer are desired to be used as the polishing particles. Particularly, the generation of the scratches is remarkably reduced, the polishing ratio with respect to the silicon oxide layer is decreased to restrain the generation of the erosion when the polishing particles include approximately 55 or more anatase type.

In addition, an amount of the polishing particles of the titanium oxide may be in a range of over approximately 0.2 wt % to approximately 10 wt % based on the total amount of the slurry. When the amount of the polishing particles of the titanium oxide is less than or equal to approximately 0.2 wt %, the polishing ratio may be too low and the polishing becomes difficult and when the amount exceeds approximately 10 wt %, a dispersing stability of the particles may be deteriorated and the size of the secondary particles may become excessively large. The amount of the polishing particles of the titanium oxide may be approximately 0.7 wt % to approximately 5 wt % based on the total amount of the slurry and may desirably be approximately 1.0 wt % to approximately 2.0 wt %. With the amount of approximately 0.7 wt % to approximately 5 wt %, the tungsten polishing rate may be good and the dispersing stability may be confirmed, and with the amount of approximately 1.0 wt % to approximately 2.0 wt %, the polishing rate of the tungsten may be better.

The oxidation promoting agent is a component to promote the oxidation of the surface portion of the tungsten and includes at least one selected from the group consisting of ferric nitrate (Fe(NO₃)₃), potassium ferricyanide, iron (III) chloride, iron (III) sulfate, iron (III) fluoride, iron (III) bromide, copper (II) chloride, copper (II) fluoride, and copper (II) bromide. The ferric nitrate will be mainly used in this application. The tungsten may be polished without applying the oxidation promoting agent, however, the polishing rate may be very low. The ferric nitrate oxidation promoting agent dissolves and is present in ultra-pure water. The amount of the ferric nitrate may be in a range of approximately 0.002 wt % to approximately 0.1 wt % based on the total amount of the slurry. When the amount of the ferric nitrate is less than approximately 0.002 wt %, the polishing rate is too low and the polishing becomes difficult. When the amount of the ferric nitrate exceeds approximately 0.1 wt %, the color of the slurry and a polishing pad may be changed. The amount of the ferric nitrate may be approximately 0.01 wt % to approximately 0.1 wt % based on the total amount of the slurry, and may be desirably approximately 0.05 wt % to approximately 0.1 wt %. Within the range of the ferric nitrate from approximately 0.01 wt % to approximately 0.1 wt %, the polishing ratio of the tungsten is good and within the range from approximately 0.05 wt % to approximately 0.1 wt %, a slurry having an optimized concentration of the ferric nitrate may be prepared to generate very low degree of dishing.

The oxidizing agent is a component to oxide the surface of the tungsten layer and includes at least one selected from the group consisting of hydrogen peroxide (H₂O₂), carbamide peroxide, ammonium persulfate, ammonium thiosulfate, sodium hypochlorite, sodium periodate, sodium persulfate, potassium iodate, potassium perchlorate, and potassium persulfate. The hydrogen peroxide is mainly used in this application. The tungsten may be polished without using the oxidizing agent, however, the polishing rated may be very low. The amount of the hydrogen peroxide as the oxidizing agent may be in a range of approximately 0.5 wt % to less than approximately 5.0 wt % based on the total amount of the slurry. When the amount of the hydrogen peroxide is less than approximately 0.5 wt %, the polishing rate is too low and the polishing becomes difficult and when the amount exceeds approximately 5.0 wt %, bubbles start to form. The amount of the hydrogen peroxide may be in a range of approximately 0.5 wt % to approximately 2.0 wt % based on the total amount of the slurry and may be desirably in a range of approximately 1 wt % to approximately 2 wt %. Within the range of the amount of the hydrogen peroxide in approximately 0.5 wt % to approximately 2.0 wt %, the polishing rate of the tungsten is appropriate and within the range of approximately 1 wt % to approximately 2 wt %, the slurry includes the hydrogen peroxide in an optimized concentration and generates very small degree of dishing. The operations of the oxidizing agent and the oxidation promoting agent are not sometimes differentiated from each other and both of them contribute to the oxidation of the surface of the tungsten.

The selectivity improving agent contributes to the increase of the ratio of the polishing rate of the tungsten and the polishing rate of the silicon oxide, that is, the polishing selectivity. Particularly, the polishing rate of the silicon oxide layer is decreased to increase the polishing selectivity. The selectivity improving agent includes at least one selected from the group consisting of polyvinyl pyrrolidone (PVP), vinyl pyridine and vinyl pyrrolidone. The PVP is mainly used in this application. The amount of the PVP may be in a range of approximately 0.05 wt % to less than approximately 3.0 wt % based on the total amount of the slurry. When the amount of the PVP is less than approximately 0.05%, dishing is generated, and when the amount is approximately 3.0 wt % or more, the polishing rate of the tungsten is low and the performing of the CMP process becomes difficult. The amount of the PVP may be in a range of approximately 0.05 wt % to approximately 1.0 wt % based on the total amount of the slurry, and may be desirably in a range of approximately 0.05 wt % to approximately 0.1 wt %. Within the amount range of approximately 0.05 wt % to approximately 1.0 wt %, the polishing rate of the tungsten is appropriate and within the amount range of approximately 0.05 wt % to approximately 0.1 wt %, the polishing selectivity is good and dishing is rarely generated.

The pH adjusting agent is added to adjust the pH of the slurry and includes an acid compound such as nitric acid. A small amount of the pH adjusting agent is used and the pH of the slurry is adjusted to the value of approximately 1 to approximately 4.

The slurry including the titanium oxide as described above illustrates quite different mechanism from the conventional slurry. A polishing mechanism will be described in detail below.

Colloidal silica has been widely and generally used as the abrasive for polishing tungsten. When a tungsten layer is polished using a slurry including the colloidal silica, a cyclic polishing as illustrated in the conceptual diagrams in FIGS. 3 a to 3 d is known to be performed. When a silicon oxide layer 110 and a tungsten layer 120 are formed on a substrate and then are polished, a tungsten oxide layer 130 is formed on the tungsten layer 120 and an abrasive of colloidal silica 200 contacts the tungsten oxide layer 130 to start the polishing. In this case, the silica particles 200 are charged with minus and have an amorphous spherical shape, and make a contact with the surface of the tungsten oxide layer 130 to polish the tungsten oxide layer 130 (FIG. 3 a). The polishing is performed until the tungsten oxide layer 130 having an initial layer thickness (H0-H1) is removed (FIG. 3 b). Then, the tungsten oxide layer 130 is formed again on the surface of the exposed tungsten layer 120 and the silica particles 200 polish the tungsten oxide layer 130 again (FIG. 3 c) until the tungsten oxide layer 130 having the second layer thickness (H1-H2) is removed (FIG. 3 d). In this way, the formation and polishing of the tungsten oxide layer 130 is repeated cyclically, and the removing process of the tungsten layer 120 (thickness change H0→H1→H2) is conducted. When the silicon oxide layer 110 is additionally polished after removing the tungsten layer 120, the spherical amorphous silica particles 200 polish the silicon oxide layer 110. In this case, the properties of materials of the polishing particles 200 and the silicon oxide layer 110 are similar and the polishing rate is fast.

In accordance with exemplary embodiments of the present inventive concept, a polishing is performed using the slurry including titanium oxide in a quite different manner. Referring to the conceptual diagrams illustrated in FIGS. 4 a & 4 b, a silicon oxide layer 110 and a tungsten layer 120 are formed on a substrate and then a slurry is supplied to perform a CMP process. In this case, a tungsten oxide layer 130 is formed on the tungsten layer 120 and at least a portion of the abrasive of the titanium oxide 300 penetrates into the inner portion of the tungsten oxide layer 130 to polish the tungsten layer 120 and the tungsten oxide layer 130. The polishing particles of the titanium oxide 300 have a crystalline polyhedron shape and are charged with plus in an acidic pH region when the slurry includes a dispersing agent. The tungsten oxide layer 130 is charged with minus in an acidic pH region when the slurry includes a dispersing agent. Accordingly, the polishing particles of the titanium oxide 300 charged with plus and having facets penetrate into the inner portion of the tungsten oxide layer 130 charged with minus and being relatively soft (hardness of approximately 5-6). A portion of the polishing particles 300 makes a direct contact with the tungsten layer 120 and the polishing is initiated and processed in this state. As the polishing process is progressed, a portion of the tungsten oxide layer 130 and the tungsten layer 120 is peeled off and the tungsten oxide layer 130 is formed again at the interface of the tungsten oxide layer 130 and the tungsten layer 120. Accordingly, the thickness of the tungsten oxide layer 130 is kept to a predetermined thickness (ΔH) while performing the polishing. In this case, the thickness of the tungsten oxide layer 130 is kept within a range of from approximately several Å to several tens of Å. In addition, the polishing particles of titanium oxide 300 has a crystalline phase, is hard and has a wide contacting area and so, a mechanical polishing is performed more intensively than a chemical polishing and the polishing rate is very fast. The polishing process is kept until the tungsten layer 120 is removed. When the silicon oxide layer 110 is additionally polished after removing the tungsten layer 120, the crystalline polishing particles of titanium oxide 300 polish the silicon oxide layer 110. In this case, the polishing particles of titanium oxide 300 have a lower hardness than the silicon oxide layer 110 and so, the polishing is processed slowly when comparing to the colloidal silica. Since the hardness of polishing particles of titanium oxide is approximately 5.5 to approximately 6.5 while the hardness of the silicon oxide layer 110 is approximately 6 to approximately 7, a polishing ability during polishing the silicon oxide layer using the polishing particles of titanium oxide is decreased. The decrease of the polishing ability reduces the generation of an erosion phenomenon due to an excessive polishing of the silicon oxide layer.

Hereinafter, results on polishing the tungsten layer and the silicon oxide layer by using slurries including the conventional colloidal silica and the abrasive of titanium oxide prepared by the same condition will be explained.

The slurry of Comparative embodiment was prepared to include approximately 1 wt % of colloidal silica, approximately 0.1 wt % of ferric nitrate and approximately 2 wt % of hydrogen peroxide, the slurry of Embodiment 1 was prepared to include approximately 1 wt % of titanium oxide, approximately 0.1 wt % of ferric nitrate and approximately 2 wt % of hydrogen peroxide, and the slurry of Embodiment 2 was prepared to include approximately 1 wt % of titanium oxide, approximately 0.1 wt % of ferric nitrate, approximately 2 wt % of hydrogen peroxide and approximately 0.05 wt % of PVP.

An object to be polished included a tungsten wafer obtained by depositing a silicon oxide layer as an insulating layer and titanium nitride to a thickness of approximately 1,000 Å, respectively, on a silicon wafer, and then depositing tungsten to a thickness of approximately 6,000 Å, and a silicon oxide layer wafer obtained by depositing a silicon oxide layer (will be referred to “PETEOS” hereinafter) by using tetraethyl orthosilicate (TEOS) as a raw material and by a plasma deposition method, to a thickness of approximately 7,000 Å on a wafer. As a polishing apparatus, poli-762 apparatus of G & P Tech Co. was used and as a polishing pad, IC 1000/Suba IV CMP pad of Rohm & Haas Co. was used. As the polishing condition, a descending pressure was 5 psi, rotating velocity of a table and a spindle, respectively, were approximately 93 rpm and approximately 87 rpm, a flowing rate of the slurry was approximately 100 mL/min. The tungsten and the silicon oxide layer were polished respectively for approximately 60 seconds. The condition of each of the abrasives and the polishing results are illustrated in the following Table 1.

TABLE 1 Comparative embodiment Embodiment 1 Embodiment 2 abrasive colloidal silica titanium oxide titanium oxide selectivity — — PVP improving agent abrasive property amorphous/ crystalline/ crystalline/ spherical polyhedron polyhedron polishing cyclic type direct direct mechanism contacting contacting type type tungsten polishing 1787.1 3720.0 2814.0 rate (Å/min) silicon oxide layer 85.7 11.2 5.3 polishing rate (Å/min) polishing selectivity 20.9:1 332.1:1 531:1 (W:SiO2)

FIGS. 5 a to 5 c illustrate graphs showing thicknesses of the tungsten layer before and after performing the polishing in accordance with positions of a substrate and polishing rate obtained by the conventional method and exemplary embodiments of the present inventive concept.

Referring to Table 1 and FIGS. 5 a to 5 c, the polishing rate of the tungsten layer is remarkably improved while the polishing rate of the silicon oxide layer is decreased in exemplary embodiments when comparing to those obtained by using the conventional colloidal silica as the abrasive. Accordingly, the polishing selectivity of the tungsten and the silicon oxide layer increases. In Embodiment 2 additionally including a selectivity improving agent, the polishing rate of the silicon oxide layer is even further decreased and the selectivity of the tungsten and the silicon oxide layer is increased much more. In addition, the polished thickness is different in accordance with the position of the object to be polished when the conventional colloidal silica is used as the abrasive and a polishing uniformity (approximately 7%) is not good (FIG. 5 a). However, the difference in polished thickness in accordance with the position of the object to be polished is decreased when titanium oxide is used as the abrasive in exemplary embodiments and a polishing uniformity is improved (FIGS. 5 b & 5 c). Particularly, the polishing uniformity is increased even further by approximately 1.5% in Embodiment 2, in which the selectivity improving agent is additionally used.

A polishing process was performed with respect to a substrate including a pattern such as a trench, etc., formed thereon. First, a substrate including a pattern is prepared as an object to be polished. Referring to FIG. 6, a silicon oxide layer 110 is formed as an insulating layer on a silicon substrate 100 and a trench 111 is formed in the silicon oxide layer 110. Then, a titanium nitride layer 121 and a tungsten layer 120 are formed on the whole surface. For example, as illustrated in cross-sectional photographic diagram taken by a scanning electron microscopy in FIG. 8, a PETEOS layer is formed as the silicon oxide layer on the silicon wafer, and trenches having a pattern width and a depth of approximately 90 nm and approximately 190˜220 nm, respectively, are formed in the PETEOS layer. Then, on the whole surface including the trenches, titanium nitride is deposited to a thickness of approximately 200 Å and a tungsten layer is deposited to a thickness of approximately 3,000 Å to prepare the wafer to be used. The polishing apparatus and the polishing condition are the same as described above.

When a substrate including a pattern is polished, at least one of a tungsten layer and a silicon oxide layer may be over etched while performing the polishing and generate dishing or erosion. Referring to a conceptual diagram for explaining the dishing and the erosion in FIG. 7, the dishing means a phenomenon of being caved in concavely when the inner portion of the tungsten layer 120 is over etched after performing the polishing process (refer to FIG. 7, D). The erosion means a degree of a step generated between a metal region and an insulating layer region not including a metal. That is, the erosion means the over etched degree of the insulating layer from an initial insulating layer (dotted lined position) (refer to FIG. 7, E).

The wafer obtained by depositing the tungsten layer on the trench patterns in FIG. 8 is polished by using the slurries obtained by Comparative embodiment, Embodiment 1 and Embodiment 2 as described above. Thus obtained results are illustrated in FIGS. 9 to 12 d. FIG. 9 is a graph illustrating polishing results on amounts of dishing and erosion evaluated and obtained after polishing the substrate including the pattern by using each of the slurries. FIGS. 10 a to 12 d illustrate photographic diagrams on the cross-section taken by a scanning electron microscopy after polishing the substrate including the pattern using the slurry obtained by the Comparative embodiment, Embodiment 1 and Embodiment 2. In order to observe the generating degrees of the dishing and the erosion and the relation between them for each of the slurries, an over etching was performed until the erosion was generated.

First, the generating degree of the dishing was weak when the polishing was performed weakly so that the erosion was rarely generated for all cases. However a remarkably large amount of the dishing was generated for the Comparative embodiment using the colloidal silica as the abrasive when comparing to the Embodiments 1 & 2. When a polishing time was prolonged to generate the erosion on purpose, the amount of the dishing was rapidly increased as the amount of the erosion increased in Comparative embodiment as illustrated in FIGS. 9 and 10 a to 10 d. On the contrary, the amount of the dishing was up to approximately 60 Å when the amount of the erosion was up to approximately 300 Å in Embodiments 1 & 2 using the titanium oxide abrasive as illustrated in FIGS. 9, 11 a to 11 d, and 12 a to 12 d. The amount of the dishing was not much increased but to the extent of approximately 100 Å even though the amount of the erosion increased. Particularly, the generation of the dishing was rarely confirmed even though the erosion increased in Embodiment 2 additionally including the selectivity improving agent, PVP.

As a result, the polishing rate or an etching selectivity was good and the polishing property on the substrate including the pattern also was good when the titanium oxide abrasive was used instead of the colloidal silica abrasive. When the selectivity improving agent, PVP was added, the polishing ratio was somewhat lowered, however, the etching selectivity was very good. In addition, defects including the dishing were rarely found in the evaluation of the polishing of the substrate including the pattern.

A preparing process of the slurry is not significantly different from the preparing process of a commonly used slurry and so, will be described in brief. A vessel for preparing the slurry is prepared and a desired amount of the polishing particles of titanium oxide controlled to a desired state is weighed and added into the vessel. Then, ultra-pure water is added into the vessel to disperse the polishing particles of titanium oxide into the ultra-pure water. Then, a desired amount of a ferric nitrate dissolved ultra-pure water solution is added into the vessel and then is stirred homogeneously. A pH adjusting agent such as nitric acid, etc. is added into the vessel and mixed to obtain a first slurry. Hydrogen peroxide and a selectivity improving agent are prepared in separate vessels and are supplied to an object to be polished with the first slurry while performing polishing. The amounts of the hydrogen peroxide and the selectivity improving agent may be controlled and supplied.

Hereinafter, a process of polishing a tungsten layer and a silicon oxide layer by changing the amount of each component of the slurry in accordance with exemplary embodiments and by using the slurry, will be described.

<Changing the Amount of Titanium Oxide>

Slurries were prepared by changing the amount of titanium oxide polishing particles and a polishing was performed as described above. The results are illustrated in Table 2. In this case, the amount of the ferric nitrate was approximately 0.1 wt % and the amount of the hydrogen peroxide was approximately 2 wt % based on the total amount of the slurry. The polishing apparatus and the polishing condition were the same as described above.

As illustrated in Table 2, the amount added of the titanium oxide polishing particles may be in a range of exceeding approximately 0.2 wt % to approximately 10 wt % based on the total amount of the slurry. When the amount of the titanium oxide polishing particles is less than or equal to approximately 0.2 wt %, the polishing rate of tungsten is too low and less than or equal to approximately 249.5 Å/min and the polishing of the tungsten becomes difficult. When the amount of the polishing particles exceeds approximately 10 wt %, a solid content is increased, a dispersing stability of particles is deteriorated, and the size of secondary particles grows excessively large. The amount of the titanium oxide polishing particles may be approximately 0.7 wt % to approximately 5 wt % based on the total amount of the slurry and desirably may be approximately 1.0 wt % to approximately 2.0 wt %. When the amount of the titanium oxide polishing particles is in a range of approximately 0.7 wt % to approximately 5 wt %, the polishing rate of the tungsten may be good and approximately 2,500 Å/min or more and a dispersing stability may be confirmed. In addition, when the amount of the titanium oxide polishing particles is in a range of approximately 1.0 wt % to approximately 2.0 wt %, the polishing rate of the tungsten may be very good and may be kept to approximately 3,700 Å/min to approximately 3,800 Å/min, and a stable CMP process may become possible.

TABLE 2 polishing rate (Å/min) TiO₂ concentration (wt %) W layer SiO₂ layer 0.1 80.9 10.3 0.2 249.5 16.4 0.3 832.9 14.7 0.5 1844.3 12.3 0.7 2564.1 18.1 1.0 3720.0 11.2 1.5 3746.4 13.4 2.0 3844.2 16.4 2.5 4151.3 21.7 3.0 4091.7 24.5 5.0 4017.4 30.1 7.0 4242.6 34.2 10.0 4101.1 38.6

<Changing the Amount of Hydrogen Peroxide>

The amount of the hydrogen peroxide as the oxidizing agent was changed and a polishing was performed with respect to tungsten and a silicon oxide layer as described above and thus obtained results are illustrated in Table 3. In this case, the amount of titanium oxide was approximately 1.0 wt % and the amount of the ferric nitrate was approximately 0.1 wt % based on the total amount of the slurry. The polishing apparatus and the polishing condition were the same as described above.

As illustrated in Table 3, the amount added of the hydrogen peroxide may be in a range of approximately 0.5 wt % to approximately 5.0 wt % based on the total amount of the slurry. When the amount of the hydrogen peroxide is less than approximately 0.5 wt %, the polishing rate of the tungsten may be too low and the polishing of the tungsten may become difficult. The polishing of the tungsten may be performed without using the hydrogen peroxide, however, the polishing rate may be too low and approximately 182.8 Å/min. In this case, the confirmation of the productivity may be difficult. When the amount of the hydrogen peroxide exceeds approximately 5.0 wt %, bubbles may start to be generated. When the amount of the hydrogen peroxide is approximately 5.0 wt %, the polishing rate may be very good and approximately 5,826.4 Å/min. However, a vigorous reaction with ferric nitrate was carried out and the starting of bubbling was observed. The amount of the hydrogen peroxide may be approximately 0.5 wt % to approximately 2.0 wt % based on the total amount of the slurry, and desirably may be approximately 1 wt % to approximately 2 wt %. Within the amount of the hydrogen peroxide in the range of approximately 0.5 wt % to approximately 2.0 wt %, the polishing rate of the tungsten was appropriate and approximately 1,300 Å/min to approximately 3,700 Å/min. Within the amount of the hydrogen peroxide in a range of approximately 1 wt % to approximately 2 wt %, the concentration was optimal and the generation of the dishing was quite small.

TABLE 3 polishing rate (Å/min) H₂O₂ concentration (wt %) W layer SiO₂ layer 0 182.8 410 0.5 1377.2 13.2 1 2447.7 11.9 2 3720.0 11.2 3 4693.2 10.8 4 5345.7 12.4 5 5826.4 11.5

<Changing the Amount of Ferric Nitrate>

A polishing process was performed with respect to tungsten and a silicon oxide layer in accordance with the method described above, while changing the amount of ferric nitrate as the oxidation promoting agent. Thus obtained results are illustrated in Table 4. In this case, the amount of titanium oxide was approximately 1.0 wt % and the amount of hydrogen peroxide was approximately 2 wt % based on the total amount of the slurry. The polishing apparatus and the polishing condition were the same as described above.

As illustrated in Table 4 below, the amount of the ferric nitrate may be in a range of from approximately 0.002 wt % to approximately 0.1 wt % based on the total amount of the slurry. When the amount of the ferric nitrate is less than approximately 0.002 wt %, the polishing rate of the tungsten may be too low and the performing of the tungsten CMP process may become difficult. The polishing of the tungsten may be possible without using the ferric nitrate. However, the polishing rate may be too low and approximately 163.9 Å/min and so, the confirmation of the productivity may be difficult. When the amount of the ferric nitrate exceeds approximately 0.1 wt %, the polishing pad may be discolored. The amount of the ferric nitrate may be in a range of from approximately 0.01 wt % to approximately 0.1 wt % based on the total amount of the slurry, and may be in a range of from approximately 0.05 wt % to approximately 0.1 wt %. Within the amount range of the ferric nitrate from approximately 0.01 wt % to approximately 0.1 wt %, the polishing rate of the tungsten may be good and in a range of from approximately 2,700 Å/min to approximately 3,700 Å/min. Within the amount range of the ferric nitrate from approximately 0.05 wt % to approximately 0.1 wt %, the concentration of the ferric nitrate may be optimized and the generation of the dishing may be very low.

TABLE 4 Fe(NO₃)₃ concentration polishing rate (Å/min) (wt %) W layer SiO₂ layer 0 163.9 15.6 0.002 1173.7 12.4 0.004 2083.1 14.5 0.006 2293.2 12.7 0.008 2682 13.1 0.01 2717.6 11.9 0.02 3191.7 11.5 0.03 3393.9 12.1 0.05 3465.1 9.8 0.07 3362.4 10.6 0.1 3720 11.2

<Changing of the Amount of PVP>

A polishing process was performed with respect to tungsten and a silicon oxide layer in accordance with the method described above, while changing the amount of PVP as the selectivity improving agent. Thus obtained results are illustrated in Table 5. In this case, the amount of titanium oxide was approximately 1.0 wt %, the amount of hydrogen peroxide was approximately 2 wt % and the amount of ferric nitrate was approximately 0.1 wt % based on the total amount of the slurry. The polishing apparatus and the polishing condition were the same as described above.

As illustrated in Table 5 below, the amount of the PVP may be from approximately 0.05 wt % to approximately 3.0 wt %. When the amount of the PVP is less than approximately 0.05 wt %, dishing may be generated largely and when the amount exceeds approximately 3.0 wt %, the polishing rate of the tungsten (approximately 153 Å/min) may be very low and the performing of the CMP process may become difficult. The amount of the PVP may be in a range of from approximately 0.05 wt % to approximately 1.0 wt % and may be in a range of from approximately 0.05 wt % to approximately 0.1 wt %. Within the amount range of the PVP from approximately 0.05 wt % to approximately 1.0 wt %, the polishing rate of the tungsten may be appropriate and in a range of from approximately 1,400 Å/min to approximately 2,800 Å/min and the polishing selectivity may be good. Within the amount range of the PVP from approximately 0.05 wt % to approximately 0.1 wt %, the polishing selectivity may be approximately 500 or more and the generation of the dishing may be rare.

TABLE 5 PVP concentraion polishing rate (Å/min) (wt %) W layer SiO₂ layer selection ratio 0 3720 11.2 332 0.05 2814 5.3 531 0.1 2678 5.1 525 0.3 2461 5.2 473 0.5 2344 5.1 460 0.7 2042 5.3 385 0.9 1672 4.7 356 1 1451 4.3 337 1.5 832 4.1 203 2 537 3.6 149 3 153 3.1 49

Although a polishing slurry used in a polishing process of a metal and a method of polishing using the same have been described with reference to the specific embodiments, it is not limited thereto. Therefore, it will be readily understood by those skilled in the art that various modifications and changes can be made thereto without departing from the spirit and scope of the present invention defined by the appended claims.

EXPLANATIONS OF LETTERS OR NUMERALS

-   -   100: substrate 110: silicon oxide layer     -   120: tungsten layer 300: polishing particles 

1. A slurry for polishing tungsten, comprising: an abrasive for performing the polishing and an oxidation promoting agent for promoting formation of an oxide, the abrasive comprising particles of titanium oxide.
 2. The slurry of claim 1, wherein an amount of the titanium oxide exceeds approximately 0.2 wt % and is approximately 10 wt % or less based on the total amount of the slurry.
 3. The slurry of claim 1, wherein the oxidation promoting agent is at least one selected from the group consisting of ferric nitrate, potassium ferricyanide, iron chloride, iron sulfate, iron fluoride, iron bromide, copper chloride, copper fluoride, and copper bromide, and an amount of the oxidation promoting agent is from approximately 0.002 wt % to approximately 0.1 wt % based on the total amount of the slurry.
 4. The slurry of claim 3, wherein the amount of titanium oxide is from approximately 0.7 wt % to approximately 5 wt % based on the total amount of the slurry.
 5. The slurry of claim 4, wherein the amount of titanium oxide is from approximately 1.0 wt % to approximately 2.0 wt % based on the total amount of the slurry.
 6. The slurry of claim 3, wherein the amount of the oxidation promoting agent is from approximately 0.01 wt % to approximately 0.1 wt % based on the total amount of the slurry.
 7. The slurry of claim 3, wherein the amount of the oxidation promoting agent is from approximately 0.05 wt % to approximately 0.1 wt % based on the total amount of the slurry.
 8. The slurry of claim 3, wherein pH of the slurry is controlled to from approximately 1 to approximately
 4. 9. The slurry of claim 3, wherein the slurry further comprises at least one oxidizing agent for forming an oxide, selected from the group consisting of hydrogen peroxide, carbamide peroxide, ammonium persulfate, ammonium thiosulfate, sodium hypochlorite, sodium periodate, sodium persulfate, potassium iodate, potassium perchlorate, and potassium persulfate, and wherein, an amount of the oxidizing agent is from approximately 0.5 wt % to less than approximately 5.0 wt % based on the total amount of the slurry.
 10. The slurry of claim 9, wherein the amount of the oxidizing agent is from approximately 0.5 wt % to approximately 2 wt % based on the total amount of the slurry.
 11. The slurry of claim 9, wherein the amount of the oxidizing agent is from approximately 1 wt % to approximately 2 wt % based on the total amount of the slurry.
 12. The slurry of claim 3, further comprising at least one selectivity improving agent selected from the group consisting of polyvinyl pyrrolidone, vinyl pyridine and vinyl pyrrolidone.
 13. The slurry of claim 12, wherein an amount of the selectivity improving agent is from approximately 0.05 wt % to less than approximately 3.0 wt % based on the total amount of the slurry.
 14. The slurry of claim 13, wherein the amount of the selectivity improving agent is from approximately 0.05 wt % to approximately 1.0 wt % based on the total amount of the slurry.
 15. The slurry of claim 13, wherein the amount of the selectivity improving agent is from approximately 0.05 wt % to approximately 0.1 wt % based on the total amount of the slurry.
 16. The slurry of claim 3, wherein the particles of titanium oxide is formed to have a crystalline phase and a mean primary particle size is from approximately 10 nm to approximately 100 nm.
 17. A slurry for polishing tungsten comprising particles of titanium oxide as an abrasive for performing polishing, the particles of titanium oxide having a crystalline phase and at least a portion of the particles of titanium oxides having an anatase crystalline phase, the particles of titanium oxide having a mean primary particle size of from approximately 10 nm to approximately 100 nm.
 18. The slurry of claim 17, wherein the particles of titanium oxide has a polyhedron shape.
 19. The slurry of claim 18, wherein the particles of titanium oxide have the mean primary particle size of from approximately 15 nm to less than approximately 50 nm.
 20. The slurry of claim 17, wherein the particles of titanium oxide comprises the anatase crystalline phase and a rutile crystalline phase, and an amount of the anatase crystalline phase exceeds approximately 50 based on 100 of a total of the anatase and the rutile crystalline phases. 21-31. (canceled) 